Formins are large multidomain proteins involved in the regulation of actin and microtubule networks during cell division and the maintenance of cell polarity. Diaphanous-related formins (Drf) are regulated by the release of an autoinhibitory interaction by a small GTPase belonging to the Rho family. The goal of my research is to define and characterize the Rho binding domain and the autoinhibitory domain of mDia1, a mouse Drf, via structural and functional studies. The mechanism of formin autoinhibition through its DAD domain and the release of this autoinhibition by Rho GTPases will be studied structurally by x-ray crystallography and functionally by a variety of methods including site-directed mutagenesis and isothermal titration calorimetry. The combination of these techniques allows for a detailed understanding of the role of formin in actin cytoskeleton regulation and maintenance.